Method for processing sulfide minerals and concentrates

ABSTRACT

Recovery of nonferrous, rare and precious metals from sulfide minerals and concentrates is described. The hydrometallurgical method of sulfide minerals and concentrates processing, involving sulfide minerals oxidation in aqueous medium using nitrogen oxides, provides that the sulfide materials containing slurry are subjected to oxidation of the sulfide which is realized under controlled conditions of the slurry acidity. Constant neutralization of sulfuric acid formed as a result of the sulfides oxidation is provided. The sulfuric acid is neutralized to acidity level, at which no formation of elementary sulfur occurs, while natural or artificial substances, such as CaC0 3 , MgC0 3 , Ca(OH) 2 , CaO, NaOH, CaHP0 4  etc., are used as acidity neutralizers. Oxidation of sulfide minerals is realized under agitation. Oxidation is realized in the range of 20-90° C., mainly in the range of 65-85° C. The liquid-to-solid ratio varies from 1:1 to 5:1, depending on effectiveness of the required precipitate formation and proceeding of the oxidation.

The method is referred to hydrometallurgical process and serves forrecovery of nonferrous, rare and precious metals from sulfide mineralsand concentrates.

The practice of sulfide ores processing is based on the fact thatessential amounts of nonferrous, rare and precious metals areconstituents of the sulfide mineral structure and cannot be extractedwithout oxidation of the sulfides. Rich ores are processed by directoxidation, while gravity- and flotation concentrates are usuallyobtained from poor ores, major amount of sulfide minerals transferringto the concentrates.

The known methods for oxidation of sulfide ores and concentrates, likeroasting, pressurized autoclave oxidation, nitric acid oxidation,bacterial oxidation, etc. have significant shortcomings, which hampertheir extensive use in current industrial practice.

The known method of hydrometallurgical recovery of metals from ores,which is described in PCT application No. 94/17216, Int. Cl..: C22B3/44, 3/06, 3/08, 3/00, 15/00, Publication Date Apr. 8, 1994, has muchin common with the invention proposed and consists in oxidation ofsulfide minerals by nitric acid. Oxidation of sulfide minerals withconcentrated nitric acid gives rise to nitric acid thermal decompositioneffect catalyzed by transition metal cations transferred into solutionfrom the concentrate. It results in the necessity to spend 3-6 weightamounts of acid of theoretically required one, which makes the oxidationunfit for economic reasons. Besides, after the concentrates oxidationwith nitric acid the solution contains a great amount of nitrates, whichimpedes their safe discharge to the environment.

There are well-known processes reducing consumption of nitric acid forconcentrates oxidation due to feed of pure oxygen to the oxidationreactor to convert nitrogen oxides into regenerated nitric acid directlyin the reactor. One of the processes is described in the PCT applicationNo. 97/11202, Int. Cl.: C22B 3/06, 11/00, Publication Date: 27 Mar.1997. However, the processes due to thermodynamic reasons involveoxidation of a portion of sulfide sulfur to elementary sulfur, whichshields the surface of gold and other precious metals and deterioratestheir further recovery.

One feature in common between the Prior Art and technical approachproposed consists in the stage of sulfide mineral oxidation by nitricacid. The action of nitric acid brings about transfer of metal intosolution, which facilitates its recovery.

The technical approach proposed describes the process, which permits:

1. Oxidation of sulfide minerals contained in ores and concentrates forsubsequent, as complete as practicable, recovery of nonferrous, rare andprecious metals (using the well-known techniques),

2. Oxidation of sulfide minerals that occurs under conditions ruling outformation of elementary sulfur with simultaneous hydrolysis of trivalentiron into compounds binding arsenic into water-insoluble form,

3. Using nitrogen oxides as a catalyst of sulfides oxidation, moreover,the regeneration of nitrogen oxides from lower valence forms into higherones is realized using either air or oxygen,

4. Using nitrogen compounds, which are catalysts of sulfide oxidation,in the most active form, i.e. as nitrous acid and its oxides.

The invention is aimed at creating conditions for the most completeextraction of metals, preventing formation of elementary sulfur.

The objective is attained by means of the following: thehydrometallurgical method of sulfide minerals and concentratesprocessing, which involves sulfide minerals oxidation in aqueous mediumusing nitrogen oxides, envisages that the sulfide materials containingslurry are subjected to oxidation of the sulfide and the oxidation isrealized under controlled conditions of the slurry acidity, i.e. withconstant neutralization of sulfuric acid formed as a result of thesulfides oxidation, moreover, sulfuric acid is neutralized to aciditylevel, at which no formation of elementary sulfur occurs, while naturalor artificial substances, such as CaCO₃, MgCO₃, Ca(OH)₂, CaO, NaOH,CaHPO₄ etc., are used as acidity neutralizers; the choice of a specificneutralizer is dictated by the necessity of formation of slurryneutralization products with assigned physicochemical properties:filterability, slurry thickening, arsenic substance insolubility,non-toxicity and other required properties. Oxidation of sulfideminerals is realized under agitation providing sufficient mass exchangeand efficient occurrence of chemical reactions. Oxidation is realized inthe temperature range of 20-90° C., mainly in the range of 65-85° C. Therequired temperature is maintained by removal of heat released duringsulfides oxidation from the oxidation reactors. The liquid-to-solidratio may vary from 1:1 to 5:1, depending on the effectiveness of therequired precipitate formation and proceeding of sulfide oxidationreactions. Nitric and nitrous acids, as well as their oxides, mainlynitrous acid, HNO₂, and its oxide, N₂O₃, are used as oxidizing agents inthis patent application. Air or oxygen is used for regeneration ofnitrogen oxides from NO to N₂O₃. Absorption of nitrogen oxides for theirseparation from the air inert nitrogen is realized by sulfur acidsolutions, their prevailing concentration 75-98%. Sulfuric aciddenitration is realized both thermally by heating mainly to atemperature not exceeding 250° C., and chemically, i.e. by introductionof denitrating substances, like alcohols, formaldehyde and otherchemical reducing agents. Absorption of nitrogen oxides for theirseparation from inert nitrogen in the air is realized in agreement,using monovalent copper salt solutions. Denitration of the monovalentcopper salt solutions is realized by dosed supply of compressed air,possibly with simultaneous heating of the solution. Monovalent coppersolutions may contain stabilizing agents impeding copper oxidation frommonovalent to bivalent one, as bivalent copper solutions are noteffective solvents of NO. The well-known substances, namely tributylphosphate and adipodinitrile, as well as reducing agents likeformaldehyde, hydrazine, etc. can be used as stabilizing agents.Nitrogen oxide regeneration process involving NO oxidation by pureoxygen is realized at a temperature of 15-25° C. in individualregeneration oxidizer, which permits converting NO into N₂O₃ andpreventing nitric acid accumulation in the slurry.

The flowsheets illustrated in FIG. 1-3 are provided for clarifying theessence of the technical approach proposed. The flowsheet in FIG. 1depicts schematically the hardware for oxidation of sulfide ores andconcentrates with nitrogen oxides regeneration by air and absorption bysulfuric acid, where:

1—sulfide ores and concentrates oxidation reactor

2—blower

3—oxidizer

4—absorber

5—denitrator

6—pump

7—fan.

Flowsheet in FIG. 2 depicts schematically the hardware for oxidation ofsulfide ores and concentrates with absorption of nitric oxide by coppersalts and regeneration with air, where:

1—sulfide ores and concentrates oxidation reactor

2—blower

3—oxidizer

4—absorber

5—denitrator

6—pump

7—fan.

Flowsheet in FIG. 3 depicts schematically the hardware for oxidation ofsulfide ores and concentrates with regeneration of nitrogen oxides withoxygen, where:

1—sulfide ores and concentrates oxidation reactor

3—oxidizer

6—pump.

DESCRIPTION OF THE TECHNOLOGICAL PROCESS

The schematic hardware block diagram for oxidation of sulfide ores andconcentrates with nitrogen oxides regeneration by air and absorption bysulfuric acid is provided in FIG. 1. Oxidation of sulfide minerals takesplace in reactor 1 equipped with a slurry stirring device. Gases fromthe reactor top section, consisting primarily of NO, enter oxidizer 3,to which from blower 2 via regulator the air enters in the amountnecessary for NO oxidation to N₂O₃. Downstream of the oxidizer nitrousgases enter absorber 4, where nitrous gas is absorbed by sulfuric acidsolution, after that nitrogen via fan 7 is released to the atmosphere,while sulfuric acid saturated with nitrous gases enters denitrator 5. Inthe denitrator as a result of heating and interaction with specialchemical additions sulfuric acid evolves nitrous gases, absorbed by theacid in the absorber, into gaseous phase, and then the gases enter thesulfides oxidation reactor. After denitration sulfuric acid is fed bypump 6 to absorber 4 for continuing the nitrous gases absorption.

The schematic hardware block diagram for oxidation of sulfide ores andconcentrates with absorption of nitric oxide by copper salts andregeneration with air is provided in FIG. 2. Oxidation of sulfideminerals takes place in reactor 1 equipped with a slurry stirringdevice. Gases from the reactor top section, consisting primarily of NO,enter absorber 4, where nitric oxide, NO, is absorbed by copper saltsolution, after that nitrogen via fan 7 is released to the atmosphere,while copper salt solution saturated with nitric oxide, entersdenitrator 5. In the denitrator as a result of NO oxidation andinteraction with special chemical additions copper salt solution evolvesinto gaseous phase nitrogen oxide, NO, absorbed in the absorber, whichenters oxidizer 3, to which air is fed from blower 2 via a regulator inthe amount necessary for NO oxidation to N₂O₃. From oxidizer 3 nitrousgases enter the sulfides oxidation reactor.

The schematic hardware block diagram for oxidation of sulfide ores andconcentrates with regeneration of nitrogen oxides by oxygen is providedin FIG. 3. Oxidation of sulfide minerals takes place in reactor 1equipped with a slurry stirring device. Gases from the reactor topsection, consisting primarily of NO, enter oxidizer 3, to which pureoxygen is fed in the amount necessary for N₂O₃ formation. Regeneratednitrogen oxides are fed by pump 6 to the sulfides oxidation reactor.

Oxidation of sulfide ores and concentrates is realized with observingand controlling the following conditions:

1. The slurry acidity is controlled so that the concentration of freesulfuric acid formed during sulfide sulfur oxidation in not in excess of10-20 g/l of the slurry. It is achieved by introducing substances, whichneutralize acidity, into the slurry. CaCO₃, MgCO₃, CaO, Ca(OH)₂, CaHPO₄,NaOH and other natural or artificial acidity neutralizers can be amongthe substances mentioned. When choosing a specific neutralizer, oneshould bear in mind the necessity to form precipitates, i.e. products ofthe slurry neutralization and trivalent iron hydration, featuring theassigned properties: thickening ability, filterability, insolubility ofarsenic, antimony compounds, and other toxic substances contained inprecipitates. The above-mentioned conditions permit oxidizing allsulfide sulfur to sulfate one without formation of the elementary form.Simultaneously arsenic, antimony and other toxic elements for theprocess and the environment are transferred to water-insoluble state.

2. The process of oxidation in the reactor is arranged so that nitrousacid, HNO₂, and its oxide, N₂O₃, are oxidizing agents, while the airoxygen is used for the acid and its oxide regeneration. For thispurpose, gases from the sulfide concentrates oxidation reactor (FIG. 1,pos. 1) consisting largely of NO, enter the oxidizing volume (FIG. 1,pos. 3), to which the air is dosed, allowance made for gas mixtureanalysis, for NO oxidation to N₂O₃ by the reactions:2N0+0₂=2N0₂N0₂+NO=N₂0₃

N0₂ formed as a result of NO oxidation by the air oxygen at atemperature below 140° C. has a tendency towards polymerization withformation of N₂0₄. Accordingly, after NO mixing with oxygen in gasphase, chemical equilibrium of N0, 0₂, N0₂, N₂O₃ and inert nitrogen ofthe air will set in.

The equilibrium constant of nitrogen dioxide polymerization

${2\mspace{11mu}{NO}_{2}} = {{{N_{2}O_{4}} + {56.8\mspace{11mu}{kJ}\text{/}{mol}\mspace{14mu}{Ka}}} = \frac{P_{N\; 2O\; 4}}{P^{2}{NO}\; 2}}$

in the range of low concentrations of NO₂ is determined by the formula:

${{Lg}\mspace{11mu}{Ka}} = {\frac{2692}{T} + {1.75\mspace{11mu}\lg\; T} + {0.00484\mspace{14mu} T} - {7.144*10^{- 6}T^{2}} + 3.062}$

If concentration C (vol. %) of NO₂>10%, the equilibrium constant isexpressed by the following empirical equations:25° C. Ka=0.1426−0.7588 C _(N2O4)35° C. Ka=03183−1.591 C _(N2O4)45° C. Ka=0.6706−3.382 C _(N2O4)

where C_(N2O4)—content of nitrogen oxides in terms of N₂O₄, mol/liter

$C_{N\; 2O\; 4} = \frac{{0.5\mspace{11mu} P_{N\; O\; 2}} + {2P_{N\; 2\; O\; 4}}}{R*T}$

where P_(NO2) and P_(N2O4)—partial gas pressure, atm.

Rate constant of N₂O₃ formation:

${{NO} + {NO}_{2}} = {{N_{2}O_{3}\mspace{14mu}{Kb}} = \frac{P_{N\; 2O\; 3}}{P_{NO}*P_{{NO}\; 2}}}$

is determined by the following empirical equations:25° C. Kb=2.105−45.63 C _(N2O3)35° C. Kb=3.673−78.11 C _(N2O3)45° C. Kb=6.88−196.4 C _(N2O3)

where C_(N2O3)—content of NO, NO₂, N₂O₄ in terms of N₂O₃, mol/liter

$C_{N\; 2O\; 3} = {0.5\mspace{11mu}\left( {P_{NO} + P_{{NO}\; 2} + {2P_{N\; 2O\; 4}}} \right)*\frac{1}{R*T}}$

Thermodynamic calculations made for gas mixtures different incomposition at various temperatures and pressures proved that it isactually impossible to select conditions permitting formation of solelyN₂O₃. The presence of nitrogen oxides like NO₂ and N₂O₄ further givesrise to formation of nitric acid in the oxidation reaction, which isundesirable in the framework of this process.

The process of present invention permits solving the problem:

For separating nitrogen oxides formed in the oxidizer (FIG. 1, pos. 3)from atmospheric nitrogen and other inert gases contained in the gasmixture, nitrogen oxides are absorbed by sulfuric acid solution in theabsorber (FIG. 1, pos. 4). During NO₂ nitrogen dioxide absorption bysulfuric acid the following reactions occur:2 NO₂+H₂SO₄=HNSO₅+HNO₃

Nitric acid, HNO3, formed in highly acidic medium of sulfuric acidinteracts with HNSO₅ by the reaction:HNSO₅+HNO₃=H₂SO₄+2 NO₂

Hence, absorption of NO₂ and N₂O₄ by sulfuric acid is inefficient, as itresults in formation of the initial substances.

Absorption of nitrogen oxides in the form of N₂O₃ by sulfuric acid isvery effective, since interaction is complete with formation of HNSO₅:N₂O₃+H₂SO₄=HNSO₅+HNO₃2 HNO₃=H₂O+N₂O₃

Thus, nitrogen oxides in the form of N₂O₃ are absorbed completely bysulfuric acid solutions.

NO solubility in sulfuric acid solution is insignificant and at atemperature of 20° C. under normal pressure it is:

H₂SO₄ concentration % 100 45 24 0 NO content % 0.0025 0.002 0.005 0.009

The data above suggest that when a mixture of gases consisting of NO,NO₂, N₂O₃, N₂O₄ and inert gases is fed to the absorber, solely N₂O₃ willreact irreversibly with sulfuric acid. Accordingly, concentration ofN₂O₃ will decrease and chemical reactions will takes place towards itsformation. The rates of gas reactions are very high and equilibrium inthe system sets in 0.1-0.5 sec, which permits absorbing nitrogen oxidesin the form of N₂O₃ in the absorber in the course of gas residence init.

3. To decrease the loss of nitrogen oxides with flue gases, stemmingfrom partial pressure of nitrogen oxides above sulfuric acid, nitrousgases absorption will be realized by sulfuric acid, its concentration75-98%. Advisability of using sulfuric acid solutions with theabove-mentioned concentration limits is dictated by the degree ofhydrolysis of nitrosyl sulfuric acid, HNSO₅, in H₂SO₄ solutions, and,accordingly, by pressure of nitrogen oxides over H₂SO₄ surface.

H₂SO₄ 98 95 92 90 87 80 70 57 concentration % % of HNSO₅ 1.1 4 7.3 12.419.4 27.7 49.8 100 hydrolysis

4. Sulfuric acid saturated with nitrous gases enters the denitrator(FIG. 1, pos. 5), where thermal and chemical decomposition of nitrosylsulfuric acid, HNSO₅, occurs with formation of the initial acid andnitrous acid, HNO₂. The decomposition takes place largely as a result ofheating, but chemical denitrating agents, like alcohols, formaldehydesand other chemical reducing agents, can also be used for sulfuric aciddenitration. High temperature (up to 250° C.) and the chemicalsubstances give rise to nitrosyl sulfuric acid and nitrous aciddecomposition with evolution of N₂O₃, which in its turn at thistemperature provides equimolar mixture of NO and NO₂. The gas mixture isfed to the oxidation reactor (FIG. 1, pos. 1), where oxidation ofsulfide concentrates stems from the effect of nitrous acid formed uponinteraction between nitrous gases and the slurry water.

For saving high-temperature energy media, which are to be used fornitrosyl sulfuric acid heating up to 250° C., copper salt solutions canbe used in the process of nitrogen oxides regeneration instead ofsulfuric acid. It is a well-known fact that aqueous solutions ofmonovalent copper salt dissolve readily nitric oxide, NO. In theflowsheet depicted in FIG. 2 waste gases from sulfide ores andconcentrates oxidation reactor (FIG. 2, pos. 1) and largely consistingof NO, are absorbed in the absorber (FIG. 2, pos. 4) by monovalentcopper salt solution. Chlorides, sulfates, ammonium and otherwater-soluble salts of monovalent copper can be used as active compoundsfor nitrogen oxides absorption. Monovalent copper solution saturatedwith nitric oxide enters the denitrator (FIG. 2, pos. 5), to which fromthe blower (FIG. 2, pos. 2) compressed air is dosed, possibly withsimultaneous heating of the solution. Nitric oxide, NO, is oxidized indissolved form to N₂O₃, that is not absorbed by monovalent coppersolution and is removed to the oxidizer (FIG. 2, pos. 3). Finalcorrection of the degree of NO oxidation to N₂O₃ form occurs in theoxidizer, after that nitrous gases are fed to the oxidation reactor(FIG. 2, pos. 1).

Denitrated solution of copper salts from the denitrator (FIG. 2, pos. 5)by the pump (FIG. 2, pos. 6) is fed for the absorber (FIG. 2, pos. 4)sprinkling. Neutral nitrogen of the air, which failed to dissolve in thecopper salt, is sucked out by the fan (FIG. 2, pos. 7) and is releasedto the atmosphere. Monovalent copper solutions may contain stabilizerspreventing copper oxidation from monovalent to bivalent one, as bivalentcopper solutions are not effective solvents of NO. The well-knownsubstances like tributyl phosphate and adipodinitrile, along with otherreducing agents, such as formaldehyde, hydrazine, etc., can be used asthe stabilizers.

When pure oxygen is used for NO oxidation in regeneration, the hardwareblock diagram is much simpler, as there is no necessity to remove inertnitrogen of the air from the system. Meanwhile, implementation of aseparate regeneration oxidizer (FIG. 3, pos. 3) is an essential elementof our new technology, as it permits regeneration by NO converting intoN₂O₃ and avoiding nitric acid accumulation in the slurry. Oxygen feedingdirectly to the oxidation reactor will give rise to parallel formationof nitric and nitrous acids, since the conditions of concentratesoxidation (65-85° C.) and conditions of nitric acid regeneration differin temperature and pressure.

Examples of specific implementation of the method claimed:

1. Copper ore featuring the composition: pyrite—80%, chalcopyrite—4%,sphalerite and galenite—1%, quartz—7%, chlorite—2%, serecite—2%, barite,epidote—up to 1% underwent oxidation according to the hardware blockdiagram depicted in FIG. 1.

Chemical composition of the ore is: copper—1.54%, zinc—0.46%,sulfur—42.4%, iron—40.6%, silicon oxide—9.8%, aluminium oxide—2.4%,magnesium oxide—0.42%, calcium oxide—0.1%, potassium oxide—0.22%, sodiumoxide—0.12%, gold—1.4 g/t, silver 13 g/t.

It took 4 hours to realize the oxidation process at the processtemperature in the oxidation reactor of 75° C. Turnover of nitric oxidein terms of NO made up 940 grams per kg of the ore in the period of theprocess conduct. Temperature in the absorber (FIG. 1, pos. 4) wasmaintained at a level of 26° C., temperature in the denitrator (FIG. 1,pos. 5)—at a level of 130° C., ethyl alcohol in the amount of 2 ml perliter of denitrated sulfuric acid solution was used for denitrationpromotion. Sulfuric acid formed was neutralized by introducing ofCa(OH)₂ into the slurry solution to the level of residual acidity 5 g/lin terms of sulfuric acid. No formation of elementary sulfur wasobserved as a result of the oxidation process under controlledconditions of the slurry acidity. According to chemical analysis datathe content of sulfide sulfur in the cake after the process completionmade up 1.6%. Transfer of copper into solution amounted to 98.5% of theinitial content in the ore, that of zinc—97% of the initial content inthe ore.

The cake was cyanidated after washing and neutralization. Gold recoverymade up 94%, that of silver—91% of the initial content in the ore.

2. Mixed flotation concentrate of the following composition:

copper—22.5%, zinc—3.9%, sulfide sulfur—40%, iron—32.6%, siliconoxide—0.5%, aluminium oxide—0.4%, lead—0.18%, organic carbon—0.22%,gold—10.6 g/t, silver 71.4 g/t, was subjected to oxidation according tothe hardware block diagram depicted in FIG. 2.

Duration of the oxidation process made up 6 hours, at the processtemperature in the oxidation reactor 80° C. Turnover of nitrogen oxidein terms of NO amounted to 1670 g/kg of ore during the period of theprocess. Temperature in the absorber (FIG. 1, pos. 4) was maintained ata level of 26° C., temperature in the denitrator (FIG. 1, pos. 5)—at alevel of 70° C., formaldehyde in the amount of 0.7 g/liter of solutionbeing used as copper chloride solution stabilizer. Sulfuric acid formedwas neutralized by introducing solution of Ca(OH)₂ to the slurry to thelevel of residual acidity of 3 g/l in terms of sulfuric acid. As aresult of the process conduct with control over the slurry acidity, noformation of elementary sulfur was observed.

According to chemical analysis data the content of sulfide sulfur in thecake after the process completion made up 2.1%. Copper transfer tosolution made up 99.1% of the initial content in the ore, that ofzinc—98.3% of the initial content in the ore.

After washing and neutralization the cake was cyanidated. Recovery ofgold proved to be 97%, that of silver—94% of the initial content in theore.

3. Pyrrhotine ore featuring the following composition:

pyrrhotine—67.2%, chalcopyrite—11.1%, pentlandite—9.5%, magnetite—5.7%,non-ore minerals—5.7%, titanomagnetite—0.2% was oxidized using thehardware block diagram shown in FIG. 3.

Chemical composition:

silicon oxide—1.6%, aluminium oxide—1.85%, iron—52.1%, sulfidesulfur—30.8%, calcium oxide—1.03%, magnesium oxide—0.33%, sodiumoxide—0.17%, potassium oxide—0.14%, manganese oxide—0.11%, copper—3.67%,nickel—4.2%, cobalt—1310 g/t, platinum—1.5 g/t, palladium—2.2 g/t.

The oxidation process was conducted for 4.4 hours, at the processtemperature in the oxidation reactor 75° C. Oxygen consumption for theore oxidation was 340 g/kg of ore during the process. Sulfuric acidformed was neutralized by introducing solution of Ca(OH)₂ to residualacidity level of 7 g/l in terms of sulfuric acid, 50 g/l NaCl beingadded to the solution for complexing properties. As the oxidationprocess was conducted with control over the slurry acidity, noelementary sulfur formation was observed. According to chemical analysisdata the content of sulfide sulfur in the cake after the processcompletion was 1.1%. Copper transfer to solution made up 94.3%,nickel—96.3%, cobalt—93.3%, platinum—91.4%, palladium—95.2 % of theinitial content in the ore.

It follows from the reasoning above that the proposed hydrometallurgicalmethod of sulfide minerals and concentrates processing differs from theknown ones, therefore, the method proposed corresponds to the “novelty”criterion. Comparison of the approach proposed with the Prior Art andother technical approaches in this field of technology permittedidentification of signs, which make the proposed approach different fromthe Prior Art, meanwhile, the differences considered are implicit, whichsuggests conclusion on compliance of the approach proposed with the“inventive level” criterion. The technical approach has industrialapplications.

1. A method of processing sulfide minerals and concentrates by oxidationof sulfide minerals in an aqueous medium using an oxidizing agent whichis one or more of nitric acid, nitrous acid and their oxides, the methodcomprising: subjecting in an oxidation reactor a slurry containing thesulfide minerals to oxidation under agitation and under controlledconditions of slurry acidity using the oxidizing agent which is one ormore of nitric acid, nitrous acid and their oxides; forming in theoxidation reactor a sulfuric acid as a result of the sulfide oxidation;constantly neutralizing the sulfuric acid in the oxidation reactor usingan acidity neutralizer to an acidity level at which no formation ofelementary sulfur occurs; removing of heat released during the sulfideoxidation from the oxidation reactor; transferring NO from the oxidationreactor into a regeneration oxidizer; regenerating N₂ ₃ from thetransferred NO using air or oxygen in the regeneration oxidizer; andtransferring the regenerated N₂O₃ into the oxidation reactor; whereinthe temperature in the oxidation reactor is maintained in a range from20 to 90° C. and wherein a liquid-to-solid ratio in the slurry in theoxidation reactor is between 1:1 to 5:1.
 2. The method according toclaim 1 in which the acidity neutralizer is one or more of CaCO₃, MgCO₃,Ca(OH)₂, CaO, NaOH and CaHPO₄.
 3. The method according to claim 1 inwhich the temperature in the oxidation reactor is maintained in therange of 65-85° C.
 4. The method according to claim 1, furthercomprising before transferring the regenerated N₃O₃ into the oxidationreactor, separating the N₂O₃, formed in said method, from N₂ byabsorbing the N₂O₃ from a mix of gases comprising N₂ and N₂O₃ into asulfuric acid solution which has a concentration in the range 75-98% ;and releasing N₃O₃ from the sulfuric acid solution thermally by heatingit to a temperature not exceeding 250° C., and/or chemically byintroduction of a denitrating substance.
 5. The method according toclaim 4, in which the denitrating substance is one or more of analcohol, formaldehyde and other chemical reducing agents.
 6. The methodaccording to claim 1, further comprising separating the NO, formed insaid method, from N₂ by absorbing the NO from a mix of gases comprisingN₂ and NO into a monovalent copper salt solution; denitrating themonovalent copper salt solution using a dosed supply of compressed air,with optional simultaneous heating of the solution.
 7. The methodaccording to claim 6 in which the monovalent copper salt solutioncontains a stabilizing agent to impede oxidation of copper frommonovalent to bivalent.
 8. The method according to claim 7 in which thestabilizing agent is one or more of tributyl phosphate, adipodinitrile,or reducing agents such as formaldehyde or hydrazine.
 9. The methodaccording to claim 1, wherein the regenerating the N₂O₃ from the NOformed in said method is performed using pure oxygen in an individualregeneration oxidizer and at a temperature of 15-25° C.